The disclosure relates generally to the field of dual drill pipe strings. More specifically, the disclosure relates to an actuator and a valve system and configurations of a valve system used with dual drill strings.
It is known in the art of subsurface wellbore drilling to use a single pipe string, two parallel pipes or two nested or concentric pipe strings. Concentric or nested pipe strings refer to a string consisting of inner pipe joints arranged within outer pipe joints connected end to end.
In concentric or nested drill strings, the inner pipe forms part of a flow bore extending from the surface to a drill bit at the lower end of the drill string. An annulus between the outer pipe and inner pipe forms part of a second flow bore extending from the surface to the drill bit. Further, it is known to provide barriers or valves (e.g., check valves) in the pipe string to prevent gas-kicks, blow-outs etc. to move to the surface during drilling operations. Drilling operations may refer to the drilling of a wellbore, including the connection and disconnection of pipe segments (joints or multiple joint “stands”) during drilling operations. The barriers may be in the form of valves in the flow bores, arranged to provide seals against uncontrolled flow, such as gas-kicks and blow-outs. The valves may be check valves allowing flow in one direction and preventing flow in the other direction.
The term “drilling” as used herein should be understood to refer to creation of a hole in the subsurface by means of the pipe string. It particularly applies for drilling in the crust of the earth for petroleum recovery, tunnels, canals or for recovery of geothermal energy, both offshore and onshore.
U.S. Patent Application Publication No. 2010/0116501 A1 discloses a backup safety flow control system for concentric drill strings. The '501 publication shows a primary annulus shutoff valve assembly and a backup annulus shutoff valve assembly in the annular bore, and a primary inner bore shutoff valve assembly in the inner bore. In addition, in case the primary inner bore shutoff valve assembly fails, the flow control system includes a backup inner bore shutoff valve by means of a valve that may be dropped from the surface through the inner bore. When the wellbore pressure is brought under control, the drill string can be removed from the well so that the backup inner shutoff valve may be removed.
Other dual drill string systems may include a valve to close both the inner pipe string proximate the bottom end thereof and the outer pipe proximate the bottom end thereof when fluid pumping from the surface is stopped. When such valves are affixed proximate the bottom end of a dual drill string, and the dual drill string is inserted into (“tripped” or “run”) the wellbore, the interior of both the outer drill string and the inner drill string will be void of drilling fluid. In other cases, the dual drill string may remain fluid filled, but pressures may be reduced therein when fluid circulation is stopped for any reason. Upon resumption of fluid flow (“circulation”), the one of the inner or outer drill string carrying the fluid under pressure from the surface will become charged with drilling fluid until an actuation pressure of the shutoff valve is exceeded. However, upon the pressure in the wellbore annulus exceeding the opening pressure of the other shutoff valve, that is, the valve which closes the fluid return path, the fluid will be exposed to an air-filled conduit or to a liquid filled conduit that has pressure lower than the wellbore pressure because on cessation of fluid circulation the shutoff valve will lock in a pressure in the return conduit that represents the wellbore pressure less fluid flow friction loss pressure. Thus, lower pressure will exist at the moment of opening the other shutoff valve. Such lower pressure may cause rapid drop in the pressure of fluid in the wellbore, which may lead to wellbore collapse and/or fluid influx from formations exposed to the wellbore.
There exists a need for a method of operating a dual drill string in a wellbore and initiating circulation without exposing the wellbore to relatively low pressure upon opening of a drill string shutoff valve.